In his defence, the 16-year-old claimed his DNA was planted at the crime scene, but the sheer volume of samples recovered left his astonishing alibi in tatters.

Forensic scientist Stuart Bailey found the accused's profile on intimate swabs taken from Alesha and on the front of her neck

The odds of it being from anyone else were more than one in a billion.

Additional samples were recovered on the child's body and clothing.

Mr Bailey said it was "highly unlikely" they had got there through anything other than direct contact.

The accused was arrested at 5pm on 4 July and driven to Helen Street police station in Glasgow where he was formally charged with Alesha's murder.

Despite what prosecutor Iain McSporran QC described as a "mountain of evidence" he compounded the family's agony by forcing them to endure a trial and blamed Alesha's father's girlfiend, Toni McLachlan, for the crime.

Innocent person

In a further twist, he agreed to testify and dismissed suggestions he was a "confident liar".

The accused repeatedly denied he was responsible and told the court: "I have never met Alesha MacPhail."

The most memorable exchange came after Mr McSporran suggested it would have been "extraordinarily wicked" for Ms McLachlan to have murdered her boyfriend's daughter.

The accused, who appeared completely unfazed by the enormity of the charge facing him, said: "I agree."

The QC then put it to the 16-year-old that the same description would apply to someone who alleged an innocent person was responsible for such a crime.

The teenager locked eyes with the prosecutor across the courtroom and replied: "It would be evil."